1. Field of the Invention
This invention relates generally to a method for shortening the length of a pulse of light, and more particularly, to a method for shortening the length of a pulse of light by selectively altering the index of refraction of an optical waveguide through which the light pulse travels.
2. Discussion of the Related Art
Different applications are known in which the generation of a pulse of light is desirable and/or required. In some of these applications, such as measurement of chemical reactions and determination of distances, it is important that the pulses of light be very short. By utilizing a very short pulse of light it is possible to view minute objects, such as molecules, before the object has had time to move. Thus, time resolution is effected by the length of the pulse. Additional applications include the ability to transfer information more effectively due to the fact that a shorter light pulse carrying information will require less space. Furthermore, by compressing a light pulse it is possible to vastly increase the pulses intensity beyond the intensity of the original pulse, and therefore, an advantage lies in the reduction in power necessary to generate the original light pulse.
In order to develop a light pulse of a length which is desirable, it generally is necessary to compress the length of the pulse after it has been generated. Different methods are known in the art for reducing the length of a pulse of light. One of those methods is generally referred to as saturable absorption in which an appropriate nonlinear absorption material is positioned in an optical path, generally within a laser cavity, such that the higher intensity portion of a light pulse spike generated by the lasing process is able to pass through the absorption material while the weaker side portions of the light pulse spike are absorbed. Consequently, only the high intensity portion, or the center portion, of the pulse of light is able to traverse the absorber, thus shortening the light pulse. This procedure, however, reduces the overall energy of the pulse of light.
A second method of reducing the length of a pulse of light involves sending the light pulse through a medium which has a varying index of refraction depending on the intensity of the pulse to develop a time-varying frequency chirp on the pulse of light. This time varying pulse can then be sent through a dispersive medium to enable the back end of the pulse to catch up with the front end. Both of the above discussed methods are better described in C. L. Tang, "Ultrashort Optical Pulses," Encyclopedia of Physics, Ed. R. G. Lerner & G. L. Trigg, NY; VCH Publishers, Inc. (1991).
The prior art light pulse shortening methods suffer the drawback of being complex and/or relatively ineffective to produce the desired results. Further, there is still a need for shortening a light pulse beyond the ability of the methods known in the art. What is needed then is a simple and effective method of shortening the length of a pulse of light. It is therefore an object of the present invention to provide such a method.